1. Field of the Invention
The present invention relates to an electronic component, a manufacturing method for an electronic component, and an electronic device, and to, for example, an electronic component, a manufacturing method for an electronic component, and an electronic device having improved solderability for mounting an electronic component onto a circuit board.
2. Description of the Related Art
Some electronic elements, such as crystal resonators and semiconductors, are made available after being enclosed in packages. Each package has outer electrodes formed thereon, and the outer electrodes are soldered onto a circuit board so that an electronic element may be electrically and physically connected to the circuit board on a package basis.
FIG. 16 is an explanatory view of a conventional outer electrode 108. The outer electrode 108 has a three-layered structure of, for example, Cr, Ni, and Au. The Cr layer has good adhesive properties on glass constituting a base 103 of a package. The Cr layer is thus formed on a bottom surface of the base 103. Formed on a surface of the Cr layer is the Ni layer for forming an intermetallic compound with Sn, which is a main component of solder. Further, formed on a surface of the Ni layer is the Au layer for preventing oxidation of Ni.
When the outer electrode 108 structured as described above is soldered onto electrodes of a circuit board, the Au layer is dissolved into the solder, and part of Ni formed on the Au layer side forms an intermetallic compound layer with Sn in the solder. The remaining Ni layer (if exist), which does not form an intermetallic compound with Sn, and the Cr layer are bonded to the circuit board through the intermediation of the intermetallic compound layer and the solder. Such a technology of using Cr in the case where a base material is glass has been proposed in each of JP 2007-528591 A and JP 2006-197278 A.
In JP 2007-528591 A, in the case where a base material is glass or the like, a Cr layer is formed as an adhesive layer. JP 2006-197278 A has proposed a technology of forming on glass an outer electrode with a two-layered thin film of Cr and Au, or a CrNi alloy and Au. On the other hand, in a case where a base material is not glass, there is known another technology of forming an outer electrode with a base layer of Ni and a surface layer of Au applied thereover for preventing oxidation, or with a base layer of Cu and a layer of Sn formed thereon.
Incidentally, the application of heat during solder bonding allows Sn contained in solder (or in an electrode coating) to form an intermetallic compound layer with Cu or Ni. The intermetallic compound layer is brittle compared with a base material, and hence has a problem of being prone to crack when applied with an external force. In addition, the intermetallic compound layer grows when heated to high temperature, and hence if the Ni layer or the Cu layer completely reacts with Sn in the solder, solder joint strength is reduced, which poses a problem that the Ni layer or the Cu layer needs to have a certain degree of thickness. If the technology of JP 2006-197278 A is utilized to form a two-layered thin film of Cr and Au as a structure containing no Ni layer, there arises a problem that solder joint strength becomes insufficient depending on a thickness of the Au layer. Further, in a case of a glass-made base, there is another problem that, as the Ni layer or the Cu layer becomes thickened, stress during the formation (plating) and stress of the film itself become so large that resistance to board bending may become insufficient.